Fluid dynamic bearing system

ABSTRACT

The fluid dynamic bearing system has at least one stationary part, and at least one rotating part that is supported rotatable about a rotational axis with respect to the stationary part. A bearing gap filled with bearing fluid is formed between mutually opposing surfaces of the stationary and of the rotating part. The bearing system includes at least one fluid dynamic radial bearing and at least one fluid dynamic axial bearing that are disposed along sections of the bearing gap. In one aspect of the invention, an annular sealing gap for sealing open ends of the bearing gap has one end connected to the bearing gap and one end connected to an annular reservoir, the outside radius of the reservoir measured from the rotational axis being larger than the outside radius of the sealing gap.

BACKGROUND OF THE INVENTION

The invention relates to a fluid dynamic bearing system, used preferablyfor the rotatable support of a spindle motor. Spindle motors supportedin this way are used, for example, for driving hard disk drives.

DESCRIPTION OF THE PRIOR ART

A fluid dynamic bearing system generally comprises at least two bearingparts that are rotatable with respect to one another and that form abearing gap filled with a bearing fluid, such as bearing oil, betweenassociated bearing surfaces. Bearing patterns that are associated withthe bearing surfaces and that act on the bearing fluid are providedusing a well-known method. In a fluid dynamic bearing, the bearingpatterns taking the form of grooved patterns are formed as depressionsor raised areas usually on one or on both bearing surfaces. The bearingpatterns act as bearing and/or pumping patterns that generatehydrodynamic pressure within the bearing gap when the bearing partsrotate with respect to one another and that gives the bearing itsload-carrying capacity. Compared to ball bearings, fluid dynamicbearings possess greater running precision and running smoothness andvery much higher shock resistance. They operate practically free ofnoise and wear since, under normal operating conditions, there is nodirect physical contact between the bearing surfaces.

Spindle motors having a fluid dynamic bearing system can essentially bedivided into two different groups, that is to say, into two differentdesigns: motors having a rotating shaft and a bearing gap that isusually open at only one end and motors having a stationary shaft and abearing gap open at both ends. A significant advantage afforded bymotors of the second group is the possibility of firmly fixing thestationary shaft not only at one end but at both ends as well to thehousing or baseplate. These types of motors thus achieve appreciablygreater structural stiffness compared to motors having a shaft fixed atonly one end.

Irrespective of the type of construction, it is necessary to introducebearing fluid into the bearing gap when the bearing is being assembled.The introduction of bearing fluid into the bearing gap is quite complex,because the bearing gap is only a few micrometers wide. Various methodsof introducing bearing fluid into a fluid dynamic bearing are known fromthe prior art.

AT 504155A2 discloses a method for filling a bearing gap with bearingfluid that is suitable for bearing gaps open at one end. Here, thebearing is filled with bearing fluid in a working area subjected tonegative pressure in that a filling device is used to introduce bearingfluid into the region of the open end of the bearing gap under theprevailing negative pressure. Air is then reintroduced into the workingarea so that, due to the prevailing negative pressure in the bearinggap, the bearing fluid is sucked into the bearing gap.

This method can also be used for bearing gaps open at both ends in thatthe bearing gap is evacuated in a working area and bearing fluid isapplied from both sides to the open ends of the bearing gap, the bearingfluid then being forced into the bearing gap when air is reintroducedinto the working area. In the case of bearings open at both ends,however, it is consistently difficult to introduce the bearing fluidinto the region of the open ends of the bearing using an appropriatedosing device. In particular, the region of the lower open end of thebearing gap is mostly hidden under the hub or bearing bush and thus hardto reach. Because the lower bearing gap opening is difficult to reach,there is the risk of contamination of the bearing with bearing fluidduring filling.

For example, JP 2005069491A discloses such a method for filling abearing gap open at both ends. Since a sealing ring that comes intocontact with the bearing fluid is used, possible contamination of thesurfaces of the bearing cannot be ruled out. In addition, the sealingring has to be cleaned after each filling process.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a fluid dynamic bearingthat is constructed so as to allow bearing fluid to be easily andreliably filled into the bearing gap.

This object has been achieved according to the invention by a fluiddynamic bearing having the characteristics outlined in independent claim1.

Preferred embodiments of the invention and further advantageouscharacteristics are revealed in the subordinate claims.

The fluid dynamic bearing system has at least one stationary part and atleast one rotating part that is supported rotatable about a rotationalaxis with respect to the stationary part. A bearing gap filled withbearing fluid is formed between the mutually opposing surfaces of thestationary and the rotating part. The bearing system comprises at leastone fluid dynamic radial bearing and at least one fluid dynamic axialbearing that are disposed along sections of the bearing gap. Moreover,sealing means for sealing the open ends of the bearing gap are provided.According to the invention, one of the sealing means comprises anannular sealing gap that has one end connected to the bearing gap andone end connected to an annular reservoir. The reservoir has an outsideradius measured from the rotational axis that is larger than the radiusof the sealing gap.

According to the invention, a reservoir for receiving bearing fluid isthus provided between the stationary and the rotating part. Thisreservoir is not to be confused with the much smaller “reservoir” formedby the sealing gap or a tapered widening of the sealing gap. In terms ofvolume, the reservoir is constructed such that it can hold the entireamount of bearing fluid that is used in the bearing. This largereservoir volume makes it possible for the bearing fluid to beintroduced at one go, the reservoir being so large that during fillingno bearing fluid is able to reach the neighboring components of thebearing and soil them.

The edges of the reservoir or the adjoining surfaces of the bearing mayadditionally be provided with a barrier film to prevent these surfacesfrom being moistened with bearing fluid.

In a preferred embodiment of the invention, the reservoir has an insideradius, measured from the rotational axis, wherein the inside radius isequal to or smaller than the inside radius of the sealing gap.

This preferred embodiment of the invention matches the equation:r _(S) <=r _(K) <r _(D) <r _(R)

According to the invention, the bearing to be filled is thus put inposition and the entire amount of bearing fluid to be filled in is fedinto the reservoir. The bearing can subsequently be removed from thefilling device and the bearing fluid found in the filling reservoir canthen slowly travel by means of capillary action right through thesealing gap into the bearing gap. This process can take well over tenminutes. The advantage here is that the actual filling process forfilling the bearing fluid into the reservoir is very fast and thebearing can then be removed from the filling device and placed at restwhere the bearing fluid can fully migrate into the bearing gap. In apreferred embodiment of the invention, the surfaces that border thefilling reservoir are slanting surfaces that facilitate the bearingfluid to flow into the sealing gap and from there to the bearing gap.Due to the slanting surfaces of the filling reservoir, no bearing fluidremains in the reservoir region.

The reservoir is thus filled only once, namely when the bearing systemis being filled with bearing fluid, whereas at other times it is free ofbearing fluid since it is located outside the sealing region of thebearing.

The sealing gap, which is disposed between the reservoir and the bearinggap, forms a capillary seal that prevents leakage of bearing fluid fromthe bearing gap back into the reservoir. The sealing gap may comprise atapered capillary seal, i.e. it may have a region that widens into ataper. In addition to the capillary seal, the sealing means may comprisea dynamic pumping seal that is marked by pumping patterns disposed onthe stationary or on the rotating bearing part.

The transition between the outside radius of the sealing gap and theoutside radius of the reservoir is preferably made at an angle greaterthan 45°. The sealing gap thus widens significantly on transition to thereservoir.

The stationary part preferably comprises a first bearing part, a shaftaccommodated in the first bearing part and a second, annular bearingpart disposed on the shaft, the two bearing parts being disposed at amutual spacing on the shaft. The rotating part preferably comprises abearing bush, or a hub having an integrated bearing bush, that isrotatably disposed on the shaft between the two bearing parts.

The bearing preferably comprises at least two fluid dynamic radialbearings formed by mutually adjacent surfaces of the shaft and thebearing bush or hub respectively that are separated from one another bythe bearing gap. The fluid dynamic axial bearing is formed by mutuallyopposing surfaces of the end face of the first bearing part and thebearing bush.

To ensure the necessary circulation of bearing fluid in the bearing gap,a recirculation channel filled with bearing fluid is provided thatconnects remote sections of the bearing gap to one another. Therecirculation channel preferably connects the sections of the bearinggap adjoining the respective sealing means to each other.

The fluid dynamic bearing system according to the invention can beprovided as a part of a spindle motor, the motor having a stator and arotor that is rotatably supported by means of the bearing system. Anelectromagnetic drive system is used as the drive.

Preferred embodiments of the invention are described in more detailbelow on the basis of the drawings. Further characteristics andadvantages of the invention can be derived from the drawings and thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: shows a section through a spindle motor having a firstembodiment of the fluid dynamic bearing system

FIG. 2: shows a section through a spindle motor having a secondembodiment of the fluid dynamic bearing system

FIG. 3: shows a section through a spindle motor having a thirdembodiment of the fluid dynamic bearing system

FIG. 4: shows a section through a spindle motor having a fourthembodiment of the fluid dynamic bearing system

FIG. 5: shows a section through a fluid dynamic bearing according to afifth embodiment

FIG. 6: shows a section through a spindle motor according to a sixthembodiment

FIG. 7: shows a section through a spindle motor according to a seventhembodiment

FIG. 8: shows a section through the sealing region of a furtherembodiment of the fluid bearing.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a spindle motor having a fluid dynamic bearing according tothe invention. This kind of spindle motor may be used for driving thestorage disks of a hard disk drive.

The spindle motor comprises a baseplate 10 that has a substantiallycylindrical central opening in which a first bearing part 16 isaccommodated. The first bearing part 16 is approximately cup-shaped inform and comprises a central opening in which a shaft 12 is fixed. Atthe free end of the stationary shaft 12, a second bearing part 18 isdisposed that is preferably annular in shape and integrally formed withthe shaft 12 as one piece. The said parts 10, 12, 16 and 18 form thestationary components of the spindle motor. At its top end, the shaft 12has a tapped hole for attachment to a housing cover of the spindle motoror of the hard disk drive. The bearing comprises a bearing bush 14 thatis disposed in a space formed by the shaft 12 and the two bearing parts16, 18 and is rotatable with respect to these parts. The upper bearingpart 18 is disposed in an annular recess in the bearing bush 14.Mutually adjacent surfaces of the shaft 12, the bearing bush 14 and thebearing parts 16, 18 are separated from one another by a bearing gap 20open at both ends, the bearing gap being filled with a bearing fluid,such as bearing oil. The electromagnetic drive system of the spindlemotor is formed in a well-known manner by a stator arrangement 42disposed on the baseplate 10 and an annular permanent magnet 44enclosing the stator arrangement at a spacing, the annular permanentmagnet 44 being disposed on an inner circumferential surface of the hub48. In principle, it is also possible to form the hub and the bearingbush integrally as one piece.

The bearing bush 14 has a cylindrical bore on whose inside circumferencetwo cylindrical radial bearing surfaces are formed that are separated bya separator gap 24 running in between. These bearing surfaces enclosethe stationary shaft 12 at a distance of only a few micrometers, at thesame time forming an axially extending section of the bearing gap 20 andare provided with appropriate grooved patterns, so that, together withthe respective opposing bearing surfaces of the shaft 12, they form twofluid dynamic radial bearings 22 a and 22 b. As an alternative, theseparator gap may also be formed in the shaft.

A radially extending section of the bearing gap 20 adjoins the lowerradial bearing 22 b, the radially extending section being formed byradially extending bearing surfaces of the bearing bush 14 andrespective opposing bearing surfaces of the first bearing part 16. Thesebearing surfaces form a fluid dynamic axial bearing 26 taking the formof an annulus perpendicular to the rotational axis 46. The fluid dynamicaxial bearing 26 is marked in a well-known manner by bearing grooves,such as spiral-shaped bearing grooves, that may be disposed either onthe end face of the bearing bush 14, on the first bearing part 16 or onboth parts. The bearing grooves of the axial bearing 26 preferablyextend over the entire end face of the bearing bush 14, in other wordsfrom the inner rim right up to the outer rim. This goes to produce adefined distribution of pressure in the entire axial bearing gap, andnegative pressure zones are avoided since fluid pressure increasescontinuously from a radially outer to a radially inner position of theaxial bearing. It is advantageous if all the grooved patterns requiredfor the radial bearings 22 a, 22 b, the axial bearing 26 and, whereapplicable, the pumping seal 36 are disposed on the bearing bush 14,thus simplifying the manufacture of the bearing, particularly themanufacture of the shaft 12 and bearing part 16. In the region of thefirst bearing part 16, a separate bearing disk 50 may be inserted. Thisbearing disk 50 may have, for example, a special coating, such as a hardcoating.

A sealing gap 34 proportionally filled with bearing fluid adjoins theradial section of the bearing gap 20 in the region of the axial bearing26, the sealing gap 34 being formed by the mutually opposing surfaces ofthe bearing bush 14 and the first bearing part 16 and sealing the end ofthe fluid bearing system at this end. The sealing gap 34 comprises aradially extending section, which is wider than the bearing gap 20 thatmerges into an almost axially extending section opening up into a taperthat is defined by an inner circumferential surface of the bearing bush14 and an outer circumferential surface of the bearing part 16.Alongside its function as a capillary seal, the sealing gap 34 also actsas a fluid reservoir and supplies the amount of fluid necessary for theuseful life of the bearing. Moreover, filling tolerances and any thermalexpansion of the bearing fluid can be compensated.

At the other end of the fluid bearing system, the bearing bush 14adjoining the upper radial bearing 22 a is designed such that it has aradially extending surface that, together with a corresponding opposingsurface of the second bearing part 18, forms a radial gap. An axiallyextending sealing gap 32 adjoins the radial gap, the axially extendingsealing gap 32 sealing the fluid bearing system at this end. The sealinggap 32 preferably comprises a pumping seal 36 and widens at the outerend preferably forming a tapered cross-section. The sealing gap 32 isdefined by mutually opposing surfaces of the bearing bush 14 and thebearing part 18.

The sealing gap 32 or the tapered end of the sealing gap widens onceagain towards the outside so that an annular reservoir 38 is formedwhose outside radius r_(R) is larger than the outside radius r_(D) ofthe sealing gap 32. In a particular preferred embodiment of theinvention, the annular reservoir 38 has also an inside radius r_(S) thatis smaller than the inside radius r_(K) of the sealing gap, so thatr_(S)<r_(K)<r_(D)<r_(R).

The reservoir 38 is free of bearing fluid and is only needed for fillingthe bearing with bearing fluid. When the bearing is being filled withbearing fluid, the reservoir 38 as well as the tapered section of thesealing gap 32 is filled with the entire amount of bearing fluidrequired for the bearing. Through capillary action, the bearing fluidnow travels through the sealing gap 32 into the bearing gap 20 rightdown to the sealing gap 34 at the other end of the bearing gap. Nobearing fluid subsequently remains in the reservoir 38 nor in theregions of the tapered section of the sealing gap 32 adjoining thereservoir.

The bearing or the reservoir 38 is covered by an annular cover 30. Thecover 30 is put over an end rim of the bearing bush 14 and attachedthere, for example, by bonding, pressing and/or welding. The innercircumference of the cover 30 may form a gap seal together with theopposing outside circumference of the shaft 12. This goes to increasethe certainty that no bearing fluid can leak out of the sealing gap 32or the reservoir 38.

Since the spindle motor has only one fluid dynamic axial bearing 26 thatgenerates a force in the direction of the second bearing part 18, acorresponding counterforce or preload force has to be provided at therotating bearing part, the counterforce keeping the bearing system inaxial balance. For this purpose, the baseplate 10 may have aferromagnetic ring 40 that lies axially opposite the rotor magnet 44 andthat is magnetically attracted by the rotor magnet 44. This magneticforce of attraction acts in opposition to the force of the axial bearing26 and keeps the bearing axially stable. As an alternative or inaddition to this solution, the stator arrangement 42 and the rotormagnet 44 may be disposed at an axial offset with respect to one anotherin such a way that the magnetic center of the rotor magnet 44 isdisposed axially further away from the baseplate 10 than the magneticcenter of the stator arrangement 42. Through the magnetic system of themotor, an axial force is thereby built up that acts in opposition to theaxial bearing 26.

To ensure continuous flushing of the bearing system with bearing fluid,a recirculation channel 28 is provided in a well-known manner. Accordingto the invention, the recirculation channel 28 is formed as an axiallyextending or slightly slanting channel in the bearing bush 14, which ispreferably disposed at an acute angle with respect to the rotationalaxis 46 of the bearing. The recirculation channel 28 connects the tworadial sections of the bearing gap 20 between the bearing regions andthe sealing regions directly to each other and preferably ends in theradially outer section of the axial bearing where the axial gap distanceis larger than the part of the radial bearing gap that is disposed inthe near vicinity of the shaft. Due to the directed pumping effect ofthe bearing groove patterns of the axial bearing 26 and the radialbearings 22 a, 22 b, there is a flow of bearing fluid in the bearing gap20 preferably in the direction of the upper sealing gap 32. What ismore, due to the effect of the centrifugal force, the bearing fluid inthe recirculation channel 28 is transported downwards in the slantingchannel in the direction of the axial bearing 26, thus producing astable circulation of fluid.

Due to the centrifugal force that acts within the channel on the bearingfluid, it is sufficient if the lower radial bearing has asymmetricbearing patterns that have an overall upwards pumping effect, i.e. thelower branches of the radial bearing patterns are slightly longer thanthe upper branches of the radial bearing. The upper radial bearing may,in contrast, be made largely symmetric.

FIG. 2 shows an embodiment of a spindle motor having a fluid dynamicbearing that is modified vis-à-vis FIG. 1. Identical parts are indicatedby the same reference numbers. For the basic particulars, thedescription from FIG. 1 applies.

In contrast to FIG. 1, the bearing surfaces of the axial bearing 26 donot have a separate bearing disk 50, but rather the bearing surface isdirectly formed by the bearing part 16.

Compared to FIG. 1, the reservoir 138 is made considerably larger andcomprises a greater volume. This is achieved in that the bearing bush114 has a recess at its upper edge having a larger outside diameterr_(R), so that the overall volume of the reservoir 138 is increased. Theadvantage of this larger reservoir 138 is that it can hold a greateramount of bearing fluid, if required, and that bearing fluid cannot leakout as easily from the reservoir 138 when it is being filled.

FIG. 3 shows another embodiment of a spindle motor having a bearingaccording to the invention that is modified vis-à-vis FIG. 1. Identicalparts found in FIG. 1 are indicated by the same reference numbers. Thedescription from FIG. 1 applies.

The first way in which the spindle motor of FIG. 3 differs from that ofFIG. 1 is that the bearing bush now forms a part of the hub 248. Thebearing bush is thus integrally formed with the hub 248 as one piece,whereas in FIGS. 1 and 2 they were two separate parts joined together.The shape of the shaft or of the bearing part 18 and the hub 248 or ofthe section of the hub that forms the bearing bush is different in theregion of the reservoir 238 and the seal 32. Reservoir 238 has a shapeapproximately the same as that of reservoir 138 in FIG. 2. The volume isrelatively large so that it can safely hold the required amount ofbearing fluid when the bearing is being filled.

FIG. 4 shows a spindle motor according to FIG. 3 in a modifiedembodiment. The description from FIG. 1 basically applies, identicalparts being indicated by the same reference numbers.

In FIG. 4, a single-piece design for the hub 348 having an integratedbearing bush is again illustrated. The sealing gap 32 is made verynarrow and compared to FIGS. 1 to 3 does not have a tapered section thatwidens outwards. Instead, the sealing gap 332 merges with its diameterr_(D) directly into the reservoir 338 in that the sealing gap widenssharply at an obtuse angle greater than 90° and merges into a reservoir338 having an approximately rectangular cross-section with the outsidediameter r_(R). Reservoir 338 has the largest volume of all theillustrated embodiments.

FIG. 5 shows a further embodiment of the invention where only thenecessary bearing components are shown in section without the othercomponents of the spindle motor. However, the corresponding referencenumbers apply as well as the description of the parts from FIG. 1.

In contrast to FIG. 1, the hub 448 is again integrally formed with thebearing bush as one piece, a reservoir 438 being formed between theshaft or the bearing bush of the hub 448, the reservoir 438 havingapproximately the same shape as reservoir 138 from FIG. 2. In contrastto the preceding embodiments of the invention, the cover 430 is designedas a simple annular disk. The cover 430 is set in a recess in the hub448 and covers the reservoir 438. In the preceding embodiments accordingto FIGS. 1 to 4, the cover was designed as a cap that was placed overthe rim of the bearing bush.

The advantage of the disk-shaped cover cap 430 compared to the othercaps lies in its ease of manufacture and machining and its flat designthat makes it possible to reduce the overall height of the motor.

FIG. 6 shows a section through a spindle motor having a fluid dynamicbearing system similar to the motors of FIGS. 1 and 2. For the basicparticulars, the description from FIG. 1 applies.

In contrast to FIG. 1, the region surrounding the reservoir 538 is givena different design. Starting from the sealing gap 32, the reservoir 538widens out to an approximately tapered cross-section. This is achieved,on the one hand, by the design of the second bearing part 518 whoseouter surface above the pumping seal 36 is slanted in the direction ofthe rotational axis 46 to form a truncated cone. The inner sleevesurface 549 of the bearing bush 514 is slanted to the same extent andpoints radially outwards. This goes to produce a tapered reservoir 538widening in cross-section. The slanted surface of the bearing bush 514is particularly important. When the bearing is being filled, the bearingfluid is filled into the reservoir 538 and sucked into the bearing gap20 by means of a vacuum found in the bearing gap 20. The slope given tothe reservoir 538 in the region of the bearing bush 514 has the effectthat the entire bearing fluid flows fully into the bearing gap 20 or thesealing gap 32 and that not a single drop remains in the region of thesewalls of the bearing bush 514 or the opposing walls of the secondbearing part 518. This means that following the filling process, theregion 549 of the reservoir 538 need not be cleansed of drops of fluid.Cleaning always brings with it the risk of removing bearing fluid aswell from the sealing region, this bearing fluid actually being neededfor the reliable operation of the bearing.

In the motor of FIG. 1, the second bearing part 18 comprises an annularsurface adjacent to the slanting surface of the conical section of thesecond bearing part 18. The annular surface is arranged perpendicular tothe rotational axis. This may bring the risk that bearing fluid remainson the annular surface after the filling procedure.

Advantageously, the second bearing part 518 of the motor of FIG. 6 doesnot have such an annular surface perpendicular to the rotational axis,so that there is no risk that drops of bearing fluid remain in thisregion. Here the equation r_(S)=r_(K) is valid.

Another difference to FIG. 1 lies in the first bearing part that isformed in two pieces and consists of an outer part 16 a and an innerbearing part 16 b connected to the outer part 16 a and receiving theshaft. The inner bearing part 16 b forms the counter bearing to thecorresponding axial bearing surface of the bearing bush 514 to createthe axial bearing 26. Contiguous to the inside diameter of the bearingpart 16 b, the shaft 512 has a step that acts as a mechanical stop.

FIG. 7 shows another embodiment of a fluid dynamic bearing according tothe invention for the rotatable support of a spindle motor. Identicalparts are indicated by the same reference numbers as in FIG. 1 and thedescription from FIG. 1 also applies unless otherwise specified.

In contrast to FIG. 1 or FIG. 6, here the radially outer peripherysurface of the reservoir 638 is formed with a radius 649. This radius649 has the same function as the slant 549 of the bearing bush 514 inFIG. 6. The radius 649 of the bearing bush 614 in FIG. 7 makes iteasier, when the bearing is being filled, for the bearing fluid to flowfrom the reservoir 638 into the sealing gap 32 and from there into thebearing gap 20. Due to the radius 649 of the periphery surface of thebearing bush 614, no drops of fluid remain in this region and there isno need to clean the region.

The second bearing part 618 of the motor of FIG. 7 does not have anannular surface perpendicular to the rotational axis as does the bearingpart 18 of FIG. 1. This avoids the risk that drops of bearing fluidremain in this region. Here the equation r_(S)=r_(K) is valid as well.

The first bearing part is again formed by an outer bearing part 16 a andan inner bearing part 16 b that also forms the sliding surface of thelower fluid dynamic axial bearing 26.

FIG. 8 finally shows a section through the sealing region of a furtherembodiment of a fluid bearing. Recognizable is the shaft 712 or thesecond bearing part 718 that represents a part of the shaft or isconnected to the shaft. The bearing bush 714 can be seen lying opposite.The shaft and the bearing bush are separated from one another by thesealing gap 732 that is proportionally filled with bearing fluid. Thereservoir 738 adjoins above the sealing gap 732. The sealing gap istapered in cross-section and opens up in the direction of the reservoir738. The reservoir 738 is closed by a cover 730 that is designed suchthat it influences the cross-section of the reservoir 738. Starting fromthe largest diameter of the sealing gap 732, the cross-section of thereservoir 738 is made larger by the design of the bearing part 718 andthe design of the cover 730. The sealing effect of the sealing gap 732is thus reinforced by the sealing effect of the tapered reservoir 738.

Identification reference list 10 Baseplate 12 Shaft 14 Bearing bush 16First bearing part 16a First bearing part (outer) 16b First bearing part(inner) 18 Second bearing part 20 Bearing gap 22a, 22b Radial bearing 24Separator gap 26 Axial bearing 28 Recirculation channel 30 Cover 32Sealing gap 34 Sealing gap 36 Pumping seal 38 Reservoir 40 Ferromagneticring 42 Stator arrangement 44 Magnet 46 Rotational axis 48 Hub 50Bearing disk 114 Bearing bush 138 Reservoir 212 Shaft 218 Second bearingpart 238 Reservoir 248 Hub 312 Shaft 318 Second bearing part 332 Sealinggap 338 Reservoir 348 Hub 412 Shaft 418 Second bearing part 430 Cover438 Reservoir 448 Hub 512 Shaft 514 Bearing bush 518 Second bearing part538 Reservoir 548 Hub 549 Slant 612 Shaft 614 Bearing bush 618 Secondbearing part 638 Reservoir 648 Hub 649 Radius 712 Shaft 714 Bearing bush718 Second bearing part 730 Cover 732 Sealing gap 738 Reservoir r_(D)Outside radius of the sealing gap r_(R) Outside radius of the reservoirr_(S) Inside radius of the reservoir r_(K) Inside radius of the sealinggap

The invention claimed is:
 1. A fluid dynamic bearing system having: atleast one stationary part, at least one rotating part that is supportedrotatable about a rotational axis with respect to the stationary part, abearing gap that is formed between the mutually opposing surfaces of thestationary and of the rotating part and filled with a bearing fluid, thebearing gap having two open ends, at least one fluid dynamic radialbearing and at least one fluid dynamic axial bearing that are disposedalong sections of the bearing gap, and sealing means for sealing theopen ends of the bearing gap, characterized in that the sealing meanscomprises an annular sealing gap that has one end connected to thebearing gap and one end connected to an annular reservoir having anoutside radius r_(R), wherein the outside radius r_(R) of the reservoirmeasured from the rotational axis being larger than the outside radiusr_(D) of the sealing gap, wherein the stationary part has a firstbearing part, a shaft accommodated in the first bearing part and asecond annular bearing part disposed on the shaft, the bearing partsbeing disposed at a mutual spacing on the shaft, and wherein the secondannular bearing part comprises a cylindrical section and a conicalsection, wherein the conical section forms a slanting surface thatborders the annular reservoir and causes bearing fluid contained in thereservoir to flow back into a sealing region.
 2. A fluid dynamic bearingsystem according to claim 1, characterized in that the reservoir has aninside radius r_(S), measured from the rotational axis, wherein theinside radius r_(S) is smaller than the outside radius r_(D) of thesealing gap.
 3. A fluid dynamic bearing system according to claim 1,characterized in that during operation of the fluid dynamic bearingsystem the reservoir is free of bearing fluid.
 4. A fluid dynamicbearing system according to claim 1, characterized in that the sealinggap forms a capillary seal.
 5. A fluid dynamic bearing system accordingto claim 1, characterized in that the sealing gap forms a taperedcapillary seal.
 6. A fluid dynamic bearing system according to claim 1,characterized in that the sealing means comprises a dynamic pumpingseal.
 7. A fluid dynamic bearing system according to claim 1,characterized in that a transition between an outside radius r_(D) ofthe sealing gap and an outside radius r_(R) of the reservoir is made atan angle of >=45°.
 8. A fluid dynamic bearing system according to claim1, characterized in that radially outer surfaces of the reservoir areslanted or curved.
 9. A fluid dynamic bearing system according to claim1, characterized in that the stationary part has a first bearing part, ashaft accommodated in the first bearing part and a second annularbearing part disposed on the shaft, the bearing parts being disposed ata mutual spacing on the shaft.
 10. A fluid dynamic bearing systemaccording to claim 1, characterized in that the rotating part comprisesa bearing bush that is rotatably disposed on a shaft between the twobearing parts.
 11. A fluid dynamic bearing system according to claim 1,characterized in that it comprises at least two fluid dynamic radialbearings that are formed by mutually adjacent surfaces of a shaft and abearing bush separated from one another by the bearing gap.
 12. A fluiddynamic bearing system according to claim 1, characterized in that thefluid dynamic axial bearing is formed by mutually opposing surfaces ofthe end faces of a first bearing part and a bearing bush.
 13. A fluiddynamic bearing system according to claim 1, characterized in that arecirculation channel filled with bearing fluid is provided thatconnects remote sections of the bearing gap to each other.
 14. A fluiddynamic bearing system according to claim 13, characterized in that therecirculation channel connects sections of the bearing gap adjoining thesealing gaps to each other.
 15. A spindle motor having a stator and arotor and a fluid dynamic bearing system according to claim 1 used forthe rotatable support of the rotor that is driven by an electromagneticdrive system.
 16. A fluid dynamic bearing system having: at least onestationary part, at least one rotating part that is supported rotatableabout a rotational axis with respect to the stationary part, a bearinggap that is formed between the mutually opposing surfaces of thestationary and of the rotating part and filled with a bearing fluid, thebearing gap having two open ends, at least one fluid dynamic radialbearing and at least one fluid dynamic axial bearing that are disposedalong sections of the bearing gap, and sealing means for sealing theopen ends of the bearing gap, characterized in that the sealing meanscomprises an annular sealing gap that has one end connected to thebearing gap and one end connected to an annular reservoir having anoutside radius r_(R), wherein the outside radius r_(R) of the reservoirmeasured from the rotational axis being larger than the outside radiusr_(D) of the sealing gap, wherein the rotating part comprises a bearingbush that is rotatably disposed on a shaft between the two bearingparts, and the bearing bush comprises a slanting surface that bordersthe annular reservoir and causes bearing fluid contained in thereservoir to flow back into a sealing region.